A so called “common rail injection” or “common pressure injection” is known as such for injecting fuel into a combustion chamber of internal combustion piston engines. In such a system the provision of pressurize the fuel and controlling the injection of fuel are functionally separated from each other. Fuel is fed by means of at least one high pressure fuel pump into a pressure supply, i.e. rail, from which it is led through separate pipes into the injector or injection valve of each cylinder. In practice, the operation of an injector is electronically controlled, for instance by means of a solenoid or piezoelectric valve, in order to obtain a sufficiently short and precise injection.
A number of the most obvious problem areas of traditional fuel feeding systems have been solved by the use of a high pressure (up to about 2200 bar) fuel supply, and electronically controlled fuel injection valves by means of which it is, for instance, possible to inject fuel into an engine cylinder several times during the same combustion stroke. In other words, the timing of the injection, the duration of the injection and the quantity of injected fuel is in clearly better control than with the fuel injection pumps of prior art, whereby also the emission levels in normal operating conditions of a piston engine have been drastically reduced.
It is known in prior art to arrange a piston engine operate by making use of two different fuels. Typically a gaseous fuel, such as natural gas is used as the main fuel and a liquid fuel, such as LFO or diesel fuel oil, is used to ignite the mixture of air and gaseous fuel present in the combustion chamber of the engine.
As an example of a fuel injection system for dual fuel, particularly gaseous and liquid fuels, EP 0778410 B1 discloses an injection valve arrangement for an internal combustion engine, especially a large so called gas diesel engine. The arrangement comprises an engine cylinder head, first valve means in the form of at least two needle valves or the like for injecting gaseous fuel directly into a cylinder of the engine. There is also a second valve means in the form of a needle valve or the like, for injecting so called pilot fuel into the cylinder in order to enrich the mixture therein for ignition. Control of the operation of the gas needle valves is arranged by means of a common control valve preferably under electrical control. In addition, the valve needles of the gas needle valves are mechanically connected to each other so that the movements thereof occur concurrently.
A piston engine operating as prime mover to run a generator for producing electricity may be adapted to use various different fuels. There is a need to provide fuel injection system for a large engine capable of using methane as primary fuel.
An object of the present invention is to provide a fuel injection unit and arrangement using the unit which provides improved performance in dual fuel piston engine particularly using liquid alcohol, such as methanol as its fuel.